1. Field of the Invention
The invention relates generally to a method and composition for, in one aspect, improving oil recovery from a reservoir. More particularly, the invention relates to composition including a fatty acid alkyl ester and methods for adding the composition to an oil reservoir to recover oil from the reservoir. Other uses are also contemplated.
2. Background Information
Crude oil or petroleum is a complex liquid mixture of hydrocarbons containing primarily carbon, hydrogen, and varying amounts of other atoms such as sulfur, nitrogen, oxygen, and others. Crude oil is recovered from subsurface oil reservoirs, wherein the oil is held within pores and voids of rock and sand, and then refined to produce a number of useful substances such as gasoline, lubricants and chemical building blocks.
FIG. 1 illustrates oil production well 110 recovering oil 130 from oil reservoir 120. Production well 110 includes a production line 125 that extends into a volume of the oil held between gas 140 at a top surface and water 150 at a bottom surface. Production well 110 is able to recover the oil from sand and rock that contains it due to pumping action of the well and native pressure of the oil within the reservoir.
Recovery of oil such as that shown in FIG. 1 is comparatively easy when the oil is light, has a low viscosity, the reservoir is full of oil, and the reservoir has a high pressure. However recovery of the oil becomes more challenging when these conditions are not met. For example, rather than light, the oil may be heavy viscous oil and/or the reservoir may be substantially depleted of oil so that the reservoir pressure has been reduced. In such situations, it may be more difficult to recover oil from the reservoir. This leaves much residual oil trapped within the reservoir as an unrecoverable resource.
FIG. 2 illustrates oil 230 wetting an outside surface of sand particles 210A-C and within two oil-filled pores 220A-B formed by the sand particles. Such oil wetting of sand may make substantial amounts of the reservoir oil difficult to recover due to strong attractions such as high surface tension forces and capillary forces holding them fixedly to such regions. It may be difficult to remove the oil from such regions by using pressure as the only driving force for removal. Additionally, when water is present external to the pores it may tend to hold the oil inside the pores.
Various enhanced oil recovery methods are known to improve oil recovery from a reservoir. FIG. 3 illustrates a steam flooding enhanced oil recover operation to improve oil recovery from a reservoir. Steam addition system 310 comprising a steam generator, a stack gas scrubber, piping, flow control elements, and a steam injection line is used to add or inject steam into oil reservoir 320. The steam heats the oil in the reservoir to reduce the viscosity of the oil and make it less resistive to flow (similarly to the way that honey or molasses flows better when heated). This may allow hot oil proximate sand particle surfaces and within pores to become sufficiently mobile relative to the sand that the oil can move toward oil production well 330 suction inlet and be recovered from the reservoir.
There are several problems associated with steam flooding. A first problem is channeling wherein steam added to the reservoir takes the path of least resistance to the oil production well by improving the recovery of the weakest attached and most available oil first. Once a route to the oil production well has been established further steam flooding has decreased effectiveness due to the easy bypass to the low pressure oil production well. A second problem with steam flooding is that it is less favorable for deep oil reservoirs with high pressures. This is partly due to the increased pressure and heating needs to make the steam suitable for the high reservoir pressures.
Accordingly, there is a need for an improved approach for improving oil recovery from a reservoir.